extra low voltage 'ring'?

[Alan Ambrose]

It seems to me we'll have more and more extra low voltage (5-48V) stuff as time goes on and I'm wondering whether anyone has considered wiring all over for that as well as 220V?

 

There is a bit of thought here:

 

https://www.theengineer.co.uk/content/product/dc-energy-metering-applications

 

and

 

https://www.mdpi.com/1996-1073/11/9/2463

 

which suggests maybe a 20%-ish saving. Particularly helpful where we already have 48V batteries for PV?

 

Any thoughts?

 

Alan

[joth]

I have 24V delivered in a few places in every room for the light switches and motion sensors, plus a few other things hang off that bus (inc the catflap!). Home automation gear is pretty much standardised on 24V. Also I'm using 24V LED strips, but these are almost all radially routed rather than off any sort of bus.

 

For everything else I rely on PoE (or a wall wart, as the obvious backstop)

 

 

[Alan Ambrose]

That sounds interesting, is it possible to describe a bit more?

 

- central PSU for 24V?

- PoE from one place only?

- what kind of wiring / cable / fusing etc for the 24V?

- you have your LED strips all wired back to a central smart switch somewhere?

 

TIA, Alan

[Carrerahill]

47 minutes ago, Alan Ambrose said:

It seems to me we'll have more and more extra low voltage (5-48V) stuff as time goes on and I'm wondering whether anyone has considered wiring all over for that as well as 220V?

 

There is a bit of thought here:

 

https://www.theengineer.co.uk/content/product/dc-energy-metering-applications

 

and

 

https://www.mdpi.com/1996-1073/11/9/2463

 

which suggests maybe a 20%-ish saving. Particularly helpful where we already have 48V batteries for PV?

 

Any thoughts?

 

Alan

I cannot really see what you would tie into this realistically.

 

Most systems that require low voltage will generate their own bus. @joth  discusses some very specific lighting controls things which any controls circuits would generally have and having some LED on a 24VDC PSU doesn't quite constitute low voltage infrastructure. 

 

I had considered a 24V supply to my living room, and some other rooms for some 24V DC lighting that could run directly from a solar charged battery circuit to give me some off-grid capability but I am just going to put my money and efforts into a off-grid 240V system. Even had I proceeded with my 24V system it would have been very home made. 

 

I design building electrical systems for a living and cannot see the benefit of a low voltage infrastructure outside of specialist environments. 

 

The Engineer article really discussed the DC micro-grid that would be formed between PV panels, inverters and batteries and datacentres are a whole different kettle of fish given IT has heaps of power supplies, so why not ditch them and just run DC buses, but very very specialist. 

 

The paper you link to is very typical of, usually South Asian students who write these frankly absurd papers on really random things for their thesis. The ideas are very much based on a shall we say, less mainstream proposition.

 

Other things to consider, SELV DC will require heavier cables, everything you bought would need to adhere to some sort of SELV convention, even if you had 4 things in a room that were ultimately SELV DC, you would find that probably they all range from 5-28V for most things, so you would still need voltage regulators and then to convert the appliance you bought to run on your DC supply. 

 

I suppose you could wire your house like a caravan and buy caravan appliances and lights?!?

 

 

 

 

Edited October 12, 2022 by Carrerahill

[JohnMo]

Sound like your spending thousands or a few hundred, to save a few pounds in running costs.

[SteamyTea]

I cannot see any advantage in this LV idea.

If it is to save money, buy one less device, or cut showering time by 10 seconds.

8

Copper has an embodied energy between 30 and 90 MJ/kg.

Taking the lowest EE and assuming you put in 5 kg of copper, that is 42 kWh.

Now my phone has a 5 AH battery.  So 0.025 kWh.

Or, before system losses, I would have to charge it 1700 hours to pay back the energy debt, that is about 2.5 months.  I doubt it has had that much charging in its, so far, 4 year life.

 

[joe90]

26 minutes ago, Carrerahill said:

I design building electrical systems for a living and cannot see the benefit of a low voltage infrastructure outside of specialist environments. 

That says it all really, I have seen this type of thread before and the end result is mostly the same, not worth it.

[Radian]

Just now, joe90 said:

That says it all really, I have seen this type of thread before and the end result is mostly the same, not worth it.

 

I've started this kind of thread before and would agree that there's a questionable financial incentive behind it. On the other hand, laid-in DC can be a convenient way of going partially off-grid without the complexities and expense of a changeover switch for the AC. I've got my routers, ethernet switches and broadband modem running off PoE adaptors with a UPS battery supply. Lighting is next on the list. 48VDC is the ideal to minimise copper losses and is very easy to step down with >95% efficiencies for lower voltage applications. And ethernet cables are ubiquitous for distribution.

[Alan Ambrose]

Well you always get good answers from this forum and often from a number of perspectives.

 

I'm planning on running CAT cable everywhere which I guess means PoE everywhere, also centrally switched LED lighting, also sensors etc (e.g. Heatmaster) on radial circuits - all back to a plant room. I'm sure there will be PV batteries - maybe in the plant room, maybe not.

 

So, that seems halfway there without trying...

 

Alan

[Carrerahill]

28 minutes ago, Radian said:

On the other hand, laid-in DC can be a convenient way of going partially off-grid without the complexities...

There is (now a "was" for me) some mileage in this if for using PV generated and battery stored power, I looked at it. I essentially have 3 PV systems, 1 on the shed, 1 on the garage 1 on the house. They are all grid-tied just now.

 

I was thinking of putting a 20A 24VDC charge controller on the garage system and using it to charge a fairly inexpensive leisure battery array, then I would run 24VDC into the house and have some 24VDC lighting, thinking being I would have created a little off-grid lighting system. Sized correctly, even in Scotland, I should never run out of battery capacity. Great free lighting. With a little imagination other things could also be tied into this system. However, after much deliberation I decided that the better long term infrastructure plan was 2 consumer units, an on grid and an off-grid. Feed the off-grid from an inverter, and add loads to it that the batteries can cope with, as the battery storage becomes more affordable I would move more and move loads over to the off-grid board until I was fully off-grid. At that point the old CU just becomes redundant. This I was saw as a smaller investment, a futureproof one in my eyes, and it lets me just stick to conventional 240V loads - it also allows me to do an automatic mains bypass on the inverter if battery voltage was to plummet. 

Edited October 12, 2022 by Carrerahill

[Carrerahill]

Just now, Alan Ambrose said:

Well you always get good answers from this forum and often from a number of perspectives.

 

I'm planning on running CAT cable everywhere which I guess means PoE everywhere, also centrally switched LED lighting, also sensors etc (e.g. Heatmaster) on radial circuits - all back to a plant room. I'm sure there will be PV batteries - maybe in the plant room, maybe not.

 

So, that seems halfway there without trying...

 

Alan

What do you mean by centrally switched LED lighting?

[joth]

1 hour ago, Alan Ambrose said:

That sounds interesting, is it possible to describe a bit more?

 

- central PSU for 24V?

- PoE from one place only?

- what kind of wiring / cable / fusing etc for the 24V?

- you have your LED strips all wired back to a central smart switch somewhere?

 

TIA, Alan

Lights switches and motion sensors are hooked up via CAT6A. This runs loxone Tree protocol on one pair, 24V on another, and misc uses on the remaining 4 cores (mostly used as binary trigger contacts). Radial to each room then point-to-point within the room.

This is from the very efficient stable 24V supply that powers the Loxone server (with fuse protection per run).

 

I mostly use 5-core 1.5mm2 for the LED strips, +24V on one core and RGBW for the other 4. The core thickness is overkill but I had a lot of it on hand and ensures I don't get any voltage drop.

This also driven centrally, but from a meaty (and very noisy) 600W PSU that just gets fired up after dark, when any of the LED fixtures has a need for power. It also drives some other constant-current dimmable fixtures.

 

The idea is either the above could be replaced by 2x AGM batteries, perhaps directly charged via PV too, but I've never prioritized making that kind of change.

 

I didn't do either the above because I was trying to future proof by pre-installing LV infrastrucutre for unknown future use cases, this was just installed out of necessity to serve the need of things I had already designed into the build.  (Much the same as the 12V distro to each room for burglar alarm sensors, I should add).

 

PoE where needed comes via a central patch panel and off a single Unifi 48 port switch. This is the only element of "future proofing" - every room has a few RJ45 outlets (and some spare cables hidden behind faceplates too) and I can quite easily power new things from that where needed.

 

 

 

Edited October 12, 2022 by joth

[SteamyTea]

1 minute ago, Carrerahill said:

What do you mean by centrally switched LED lighting?

Not like my house I hope.  The light switch is not near the main door, but on the opposite wall.

Probably designed that way by an architect, who knew he would never live in the place. 

[Carrerahill]

2 minutes ago, joth said:

It also drives some other constant-current dimmable fixtures.

Constant current or constant voltage? If the former, are you taking 24VDC into a little CC driver before feeding the luminaire?

[Alan Ambrose]

>>> What do you mean by centrally switched LED lighting?

 

Something similar to joth's set-up rather than direct mains light switch -> light bulb wiring

 

Yeah they need to work, but Quinetic switches which sparkys are using to avoid tricky cable runs are part way there. Loxone more so.

 

Alan

[joth]

8 minutes ago, Carrerahill said:

Constant current or constant voltage? If the former, are you taking 24VDC into a little CC driver before feeding the luminaire?

 

LED strips are CV, the other things are all CC.

EItherway, the luminaires all connect directly to the (unswitched) +24V supply but the negative terminal returns back via a dimmer (in the central-cabinet next to the PS).  The dimmers all apply the PWM on the negative supply (so "common anode" right?).

Mostly DMX driven LED drivers e.g.

CV: https://www.aliexpress.us/item/32824271209.html

CC: https://www.aliexpress.us/item/4000473275297.html

 

 

Edited October 12, 2022 by joth

[Carrerahill]

18 minutes ago, joth said:

 

LED strips are CV, the other things are all CC.

EItherway, the luminaires all connect directly to the (unswitched) +24V supply but the negative terminal returns back via a dimmer (in the central-cabinet next to the PS).  The dimmers all apply the PWM on the negative supply (so "common anode" right?).

Mostly DMX driven LED drivers e.g.

CV: https://www.aliexpress.us/item/32824271209.html

CC: https://www.aliexpress.us/item/4000473275297.html

 

 

Yes, right, I see what you have done. 12-24VDC input drivers/power supplies.

 

 

[Alan Ambrose]

@joth - so you have radial 12V, 24V and 'active' PoE into each room?

 

Goodness 'PoE' seems a mess atm. Did you consider 5V for charging or is that a step too far?

 

Any recommendations gained from your experience of doing all that - or is that just the best solution?

 

Alan

 

 

Edited October 12, 2022 by Alan Ambrose

[joth]

40 minutes ago, Alan Ambrose said:

@joth - so you have radial 12V, 24V and 'active' PoE into each room?

 

 

LOL, yes I guess I do.

 

12V is dedicated to the alarm system. That's class 2 and professionally managed so completely out of bounds to my own tinkering. 

24V is for home automation and LV lighting, all speced and installed by myself.

 

48V is active PoE is on an as-needed basis, but of them all can most easily be added to any room where it isn't already by just swapping a patch cable or perhaps terminating a spare (hidden) CAT6 drop into an RJ45.

 

I wouldn't distribute 5V to rooms as (a) those loads tend to be quite high (e.g. phone/laptop charging) so the power line losses far too high, (b) increasingly (especially from 2024) any respectable USB charging is USB-C so multi-voltage, and (c) it's now fairly easy  to put a USB outlet on the end of a PoE cable. I would expect multivoltage PoE to USB-C adapters to become available soon.

TBH the main use I've had for this so far is putting LV outlets into the bathroom where mains is not permitted (i.e. my equal parts loved yet maligned PoE powered toothbrush charger)

 

I've found active PoE to be reliable and compatible, no issues at all. I mostly keep to Unifi gear, except for IP cameras which are mostly dahua.

 

  

40 minutes ago, Alan Ambrose said:

Any recommendations gained from your experience of doing all that - or is that just the best solution?

 

 

If I was doing it again, I'd probably do exactly the same TBH. So for me personally, yes this is my best solution.

I bit more systematic about where I put CAT6 (and spare CAT6) drops wouldn't hurt.

Questionable whether I'd do the professional installed alarm, but that's OT for this conversation.

 

I'd put more effort into selecting and matching centrally located drivers for the constant current fixtures; I ended up with more than I would like hung from 240V AC driven drivers located next to the fixture, which don't perform anywhere near as well as the direct DMX to 24V dimmers do. But again this is borderline OT for this conversation.

 

I'd not make any more infrastructure for adhoc LV consumer electrics.

 

It'd be nice if someone made aesthetically pleasing PoE to RJ45 + USB-C face-plates. Tplink do ones with integrated Wifi AP which is nice, but just needs the USB outlet to be perfect. (I'd seriously consider TP-link for everything if doing it again).

 

 

Edited October 12, 2022 by joth

[Alan Ambrose]

>>> my equal parts loved yet maligned PoE powered toothbrush charger)

 

Love it - somebody has to

 

Thanks for taking the time both to describe your set-up and your thoughts on (not much) improving it. That's where this forum is so great.

 

Alan

[MortarThePoint]

I've just found this thread looking for one I thought I had started on 48V lighting but can't find.

 

On 12/10/2022 at 14:24, joth said:

24V is for home automation and LV lighting, all speced and installed by myself.

I have a couple of questions (I'm learning):

1. Why 24VDC rather than 48VDC?
2. Where do you get your bulbs? I have seen lots of 24VDC strips, but not bulbs
3. Bulb fittings, I would like to use standard bayonet or threaded bulb fittings

I am an electronics engineer and would like to go all the way and make my own custom driver/control PCBs and wireless switches too, perhaps even lights. Bluetooth or Zigbee rather than WiFi. This means I could have no wire running from the light to the switch (good for a retrofit) and with a Li-SOCl2 coin cell I can have 15 years of battery life. All lights can then be locally controlled by a wall switch, centrally controlled by home automation as well as phone/tablet controlled.

 

If you are worried about cost, a light switch, back box, oval conduit and 4m of 1.5mm 3-core probably costs about £10 depending on tastes. A wireless switch and controller probably about the same off-the-shelf.

 

I had thought to go with 48VDC to minimise voltage drop and because it seems to be the most common voltage used by server style battery banks (based on a very quick look).

 

On 12/10/2022 at 12:16, Carrerahill said:

I design building electrical systems for a living and cannot see the benefit of a low voltage infrastructure outside of specialist environments.

I see the main benefits of a SELV system (24VDC or 48VDC) as:

1. I can play with it outside of Part-P and other regulations [TBC and for how long]
2. A single high quality regulated supply in place of lots of distributed LED drivers each of which is lower efficiency, gets hot and has to be found space for.
3. I can make my own lights. I have the technical capability to do this for mains too, but that would be much more of a regulatory headache. Designing my own 48VDC (or 24VDC) light bulb electronics would be quick, the hard bit would be the fitting.
4. Automation opportunities. Plenty of this for mains powered lights too.
5. You wouldn't start here. If you were designing a lighting approach from scratch (no prior restrictions) I think this is where you would end up.
6. Safety (ish)

[RobLe]

By accident*, we have some old car batts charged up by 600W of solar panels, and available as 12V and USB charging in a couple of rooms.  I even fitted a wall plate with car cigarette lighter type sockets in it - the idea is that there are lots of 12V useful things out there that could plugin.  So it's got a USB C charger in it - in a power cut we'd get a bit of light, and be able to charge a laptop.  I like the resilience nature of it, but I'm not sure It's worth any more effort.  It's also wasteful of PV; most of the time there is spare unused capacity.  Went for 12V, as I had 1 batt free first, then another, it's not like we have heavy loads for it.  They're independently fused then paralleled.

 

My prediction for the future of elec lights wiring by the way, is that lights won't be hard wired to wallswitches.  As MortThePoint mentioned, you can make a switch last almost forever with a battery in it.... it will be cheaper to do that than wiring it in. 

 

*free batts, and at the time wasn't allowed to wire any more PV into the mains.

[SteamyTea]

1 hour ago, MortarThePoint said:

Safety

How are you going to deal with thermal safety. 

Really needs special testing and hard to make intrinsically safe.

[MortarThePoint]

38 minutes ago, SteamyTea said:

How are you going to deal with thermal safety. 

Really needs special testing and hard to make intrinsically safe.

Not so sure what you mean about thermal safety, but some thoughts (48VDC):

1. Wiring: Similar current limits will apply, though perhaps a factor of Sqrt(2) will come into play (DC vs AC), so de-rate On Site Guide figure by say 33%. I expect if limited to 5A / 7A, you'd be OK in all installation methods with 1.0mm2 / 1.5mm2 and have up to 240W / 336W of light at your disposal with out any diversity, probably double with diversity. 240W is something like 30no. 8W bulbs or 75m of LED strip.
2. DC:DC converters: A DC:DC converter could run with an efficiency >95%. If 90% efficient and a 9W light, you need to dissipate 1W of heat. Radiative heat loss alone would get rid of 1W from around 5cm x 5cm at 75C (22C ambient), but that wouldn't be the only heat loss method. [Note: 75C is hotter than the PVC allows] Convection if open will probably dominate and conductive if a spot will help. I haven't really run any proper calculations on this, but it feels manageable.
3. Intelligence: Average power would be in the uW range when light not on. When light on, it would be dominated by the relay (if not MOSFET controlled) and likely 0.1W.
4. Local Switch: like a Bluetooth remote so power in uW range.

 

The low voltage itself goes a long way. What are you thinking of for the intrinsically safe? To have it as a product you'd have to do EMC testing etc.

 

Edited January 16, 2023 by MortarThePoint

[SteamyTea]

26 minutes ago, MortarThePoint said:

Not so sure what you mean about thermal safety

Making sure it cannot get too hot.

26 minutes ago, MortarThePoint said:

What are you thinking of for the intrinsically safe

Keeping the temperature safely below the combustion temperature of all the nearby materials.